The present invention relates to the field of coal processing. More specifically, the invention relates to the recovery of coal fines which are traditionally regarded as waste by-products of various coal processes or coal handling.
The generation of coal fines during the processing of coals and while coal products are being transported has long been an industry problem. The tendency for coal and related products to randomly fracture into particles has never been successfully regulated such that grinding processes result in a wide distribution of particle sizes. Similarly, the transport or handling of coals has the effect of inducing contact between larger pieces and results in the creation of fines.
The typical methods for handling these fines usually depend on systems customized for coal fines. Thus in those facilities where fines are being generated routinely, many are handled through slurry or hopper systems and are directed to settling ponds. The accumulations in these ponds are dealt with en masse. In the transport of coals, the fines will fall to the bottom of the transport container. In cases such as ship transport, the level of fines accumulating in the bottom of the hold can lead to conditions where spontaneous combustion can take place. This feature of waterborne shipments of coal has lead to sensitivity in the duration of shipments and as to the type and design of the vessel carrying the coal.
Recognition of the value of coal fines as an energy and chemical resource is long standing. The difficulty to date has been the poor economics involved in reprocessing the fines to a usable state or the lack of compatible and consistent outlets for coal fine consumption. The present invention has been successful in producing a usable coal product from coal fines while maintaining an economic advantage.
Other processes are known where coal fines are subjected to various conditions, typically high heats and/or pressure, and then are mechanically compressed or formed into pellets or briquettes. These processes are suited to low throughputs or batch operations and have energy or equipment requirements that make them unattractive for most of the situations described above.
One process is known where the coal fines are subjected to solvents that cause a partial and selective organic extraction to occur. The coal fines used in this process are preferentially those with paraffin content such that the relatively sticky compounds trapped in the coal matrix are brought to the surface of the coal particles. In this manner the particles are made to stick to each other and create clusters or clumps. Obvious drawbacks to this process include the required restriction of applying the solvents to certain coals. Most coal fines generated would not possess the requisite constituents for this process.
A need for a low cost method for the recovery and handling of coal fines has remained until the development of the present invention. As such it is at least one object of the present invention to provide a method for agglomerating coal fines as generated from many different sources. In addition, the method has significant economic advantages over past attempts in this field in that little energy input is required and much of the process chemistry is recycled.